For the purpose of saving energy, reducing CO2 emissions and the like, electromagnetic motors call for higher performance, such as size and weight reduction, high efficiency, high torque and high output power, and the performance is dramatically improving day to day.
Electromagnetic motors can be roughly classified into (1) radial flux motors, (2) axial flux motors, (3) and transversal flux motors, according to the direction of magnetic flux. Of these flux motors, the radial flux motor is particularly excellent in cost performance and has conventionally been used widely in a variety of products in industry as a typical machine element of a versatile actuator. The axial flux motor has a structural feature that it can be adapted to complex three-dimensional magnetic paths, but laminated steel plates which are conventionally widely used are hard to use for it. The axial flux motor is used as, in particular, a medium/large-size thin motor of a large bore diameter.
The transversal flux motor has the following structural feature. It includes a rotor and an armature (having a split toroidal core structure) as basic units. The rotor includes permanent magnets. The armature includes a toroidal coil formed around the rotation axis of the rotor and a plurality of substantially U-shaped stator cores (referred to as U-shaped stator cores hereinafter) which are provided circumferentially around the rotation axis to surround the toroidal coil. Two or more basic units are provided on the rotation axis and with a given relative phase angle around the rotation axis. With this structural feature, high torque can be achieved by the multi-polarity and a high-efficiency magnetic field can be generated relatively easily by the split toroidal core structure. In other words, in general, the transversal flux motor can be easily made to have multi-polarity since it is sufficient if a plurality of U-shaped stator cores are circumferentially arranged around the rotation axis, compared to the radial flux motor and the axial flux motor which needs a dead space for, for example, assembling and inserting a stator core with a plurality of slots arranged around the rotation axis, and a coil wound on the slot portions. Furthermore, the armature including a toroidal coil and U-shaped stator cores has a structure that makes it hard for magnetic flux to leak from the coil to the outside, thus increasing the efficiency of generation of a magnetic field due to the coil. Therefore, the transversal flux motor can be expected to be smaller than the radial flux motor and the axial flux motor.
Reduction in manufacturing costs has been demanded of electrical machines.